Maximizing light efficiency in high-speed confocal line-scanning imagers

Imaging the living human eye requires high-speed and light-capture efficiency of photons returning from the eye to increase the signal-to-noise ratio while minimizing light exposure. Here, we report the optical design of a high-speed <i>en face</i> imaging approach applied to a line-scanning laser ophthalmoscope with extremely high optical efficiency. Utilizing the asymmetry involved in scanning a line through a slit pupil and collecting light scattered from a target with the full pupil, we construct an asymmetric scanning system, delivering essentially diffraction-limited performance while projecting almost all light from the source onto the target and collecting 98% of the light returning from the target onto the detector. This compares to traditional systems using beam splitters, which require powerful light sources to maximize light collection or balance illumination and detection efficiencies.